Hydraulic pumping jack control



Nov. M, 1952 l. M'. WHITE i HYDRAULIC PUMPING JACK CONTROL Filed June 12, 1948 k w lg n w nir L" LNH Q Patented Nov. 11, 1952 HYDRAULIC PUMPING JACK CONTROL Ira Morgan White, Berkeley, Calif., assignor to The Pelton Water Wheel Company, San Francisco, Calif., a corporation of California Application .lune 12, 1948, Serial No. 32,629

'l Claims. (Cl. 60-52) My invention relates to hydraulic pumping jacks including mechanism adapted to be attached to a deep well pump for reciprocating the pump rod in a carefully controlled manner. Hydraulic pumping jacks are coming increasingly into successful use as oil wells need to be pumped in increasingly great depths. The pump is located adjacent the bottom of the well, perhaps ten or eleven thousand feet from the surface, while the jack itself is located at the surface and the jack and pump are then interconnected by an extensive metallic rod. It has been found by protracted experience that this rod because of its metallic and consequently somewhat elastic nature, is prone to break if excessive stress is imposed upon it. A breakage of the sucker rod is of great financial consequence, not only because of the loss of pumping time, but also because of the difculty in recovering or retrieving the broken mechanism and its replacement or repair. It therefore is highly important to provide a very close and careful regulation of the operation of the jack with respect to the sucker rod so that strain over an allowable amount does notA occur. It has likewise been found in practice that while one mechanical arrangement may operate quite satisfactorily under some conditions of operation, especially under some temperature conditions of operation, it may not be entirely satisfactory under other temperature conditions. In hydraulic jacks, the Working fluid is an oil, the viscosity of which varies with temperature. The pumping jacks are installed often in remote locations and are completely exposed to the atmosphere so that they function at ambient temperatures, for example from below 40 degrees to 115 or more degrees Fahrenheit. Even under these conditions, substantial variations in the application of force to the sucker rod are not permissible.

It is therefore an object of my invention to provide a hydraulic pumping jack in which the control of the jack is substantially the same under all operating conditions.

An additional ob-ject ofthe invention is to provide a hydraulic pumping jack control which is reliable under operating conditionsv to produce the desired or predetermined operation of the jack mechanism.

An additional object of the invention is to provide a timing means for regulating the operation of the pumping jack somewhat independently of the reciprocation of the jack itself.

A further obiect of the invention is in general to improve pumping jacks and especially their control mechanisms.

A further object of the invention is to provide a pumping jack control system which can readily be varied in timing by a simple variation in the structure.

Another object of the invention is to provide a pumping jack which is consistent in its operation over wide ranges in temperature and other operating conditions and yet is of a type which is generally acceptable.

Other objects together with the foregoing are attained in the v embodiment of the invention described in the accompanying description and illustrated in the vaccompanying drawings in which:

Figure 1 is a diagram showing a pumping jack control mechanism in accordance with my invention and disposed in one extreme position, most of the parts included in the diagram being disclosed in cross-section on median planes.

Figure 2 is a view similar to Figure 1 but showing the mechanism in a different extreme position with some of the parts being shown diagrammatically in side elevation rather than in cross-section.

In its preferred form the pumping jack control system of my invention comprises an actuating cylinder adapted to be reciprocated between extreme positions and to be connected by a sucker rod to the pump. The cylinder or jack is connected to a balancing tank containing operating oil and air and is alternately supplied with or deprived of oil through an oil pump and valve structure which is effective to impart opposite directions of reciprocation to the pumping jack. The hydraulic system includes a main valve for governing flow to and from the jack, the main valve itself being operated in response to the functioning of a pilot valve. The pilot valve is provided with a supply of operating fluid', not from the main pump but rather from an auxiliary pump so that flow to operate the main valve through the pilot valve is in response to the operation of the auxiliary pump.

While the pumping jack and control can be incorporated in numerous different ways and can incorporate sundry variations depending upon the environment in which it is `to be particularly utilized, it has been satisfactorily and successfully embodied in commercial use substantially as diagrammatically disclosed herein. y

As first Shown in Figure 1 in which' the mechanism is undergoing a downward movement, there is provided a pumping jack cylinder which is appropriately mounted and is of the general type shown in my co-pending application vfiled October 30,1945, Serial'No. 625,502, now Patent No. 2,562,837 issued July 31, 1951. Within the elongated cylinder 6 is a reciprocable piston 1 connected to a polish rod 8 extending from the cylinder at its lower end and connected to a pump, not shown, disposed many feet below the piston 1 in an oil or comparable well. As the piston 1 descends, .it carries the weight of the connected pump and rodwith it and consequently presses with such weight upon a body of oil in the compartment 9 below the piston. However above the piston 1, the compartment I is subject to substantially atmospheric pressure, since it is connected through apertures I2 with an overflow chamber I3 joined by avpipe I4 vtothe-upper portion of an auxiliary oil tank I6. A `check valve I1 is interposed in the pipe I4 so that no sub-atmospheric pressure can be imposed lupon the tank I6, but so that the pressure in the chamber I0 cannot greatly exceed atmospheric.

.As the piston 'I descends, it-eventually uncovers one of a group of stroke-limiting valves I8, lI9 and'2 respectively, which are all substantially identical and which are connected to the cylinder 6 by interposed pipes 2I. The valves I8, I9 and'20 are manually controlledand but one of them at atime is left open. The others remain closed. Consequently, the open one of the valves is effective to communicate the pressure conditions within the cylinder 6 through any one of the lines 22, 23 and '24 ito a connecting line 26. Intheline 26 isacheck valve 21 which permits flow in the direction of the cylinder 6 but not in the contrary direction. The pipe 26 is itself joined. to aduct `281that continues to a valve 29 carrying a'handlefl so that the valve can be variously positioned. In 'the location shown in Figure l, the valve 29 aiords access from the pipe 28 .through a pipe 132 with a chamber 33 ,at one end of a pilot valve generally designated 34.

.Within the pilot valve, there is a valve bobbin 36 reciprocable between .the extreme right hand position shown in Figure l and an extreme left hand position shown in Figure 2. At the .right hand end ofthe pilot valveand opposite to the bobbin 36 is a relativelysmaller bobbin 31, operablein a chamberi38 connected bya conduit 39 to a pipe.4l, extendingintothe side of a storage or .balancing.tanki42. This tank-has a body of jack operatingl oil1431in`the lower .portion thereof y and extending ,toa convenient level .44 and `in the upper part containsa'body 46 of air. Since the oil `43 is under pressure, the ,air 45'is likewise under pressure, and-this pressureis conveniently an average or mean ,pressure lbetween `the load on thejack piston 1 whenitis going up andthe load upon it vwhenitis going down.

'.The result of .this mechanism as so far described is that the bobbin 31 has a relatively high ortankpressure.exerted upon it, while the bobbin 36 is subject tothe lower pressure in the compartment 33 emanating from the chamber 9 the pressures differing by the pump increment. Since thebobbin vv36is largerthan the bobbin 31, the auxiliary valve -or pilot valve occupies its right hand position as shown in Figurel. '-W hen, howeventhezpiston 1 4uncovers whichever one of the valves I8, I9 and 20 iis operative, fthe high pressure below thepistongives way to the substantially atmosphericpressure vabove the. piston and this then permits the chamber 33 to discharge through the pipe .32 and the valve 29 and-through the conduit .28 and the check valve 21 to the chamber I0 above the piston. Since thepressure on the auxiliary valve through the pipe 39 from the `tank '42 onto the bobbin 31 still exists, thebobbin is immediately transferred to its other extreme position as shown in Figure 2, and a different portion of the cycle of events takes place.

But prior to the actual shifting of the auxiliary or pilot valve from its Figure l position into its Figure 2 position, and while the valve is in its Figure 1 position, it governs ,the operation of a main valve, generally designated 5I. The main valve itself comprises a housing 52 having a shuttle, generally designated 53, reciprocable therein between two extreme positions as shown in Figures 1 and 2, the shuttle being in its left hand extremeposition in Figure 1 and is in its right hand extreme position in Figure 2. The

:purposeof the ,main valve is to direct oil ow to and from a pump 54. This is the main actuating oil pump and is Adriven by a relatively heavy source of power such as an independent internal combustion engine or a relatively large electric motor v55. The pump transfers oil from two pumpinlets 5.6.and 51 through a discharge pipe 58 into amedianport 5,9 in the housing of the main valve 5I. When the valve shuttle is positioned as shown in vFigure 1, oil ows through the vhousing 5I between valve lands 6I and 62 therein and discharges through an outlet 63. One branch 64 of the outlet is blocked to oil flow since thebobbin 36 occupiescne of its connections 61 and thehand valve 29 occupies its otherconnection 68. The only other path 4for the oilisthrough a conduit 69 extending to an inlet fitting .1I .on the tank A42. This fitting is substantially the same as shown in my said Patent No. 2,562,837. .The eiect of the tting 1I in its normal position with its poppet valve 12 open, is to permitflow of liquidbackinto the tank 42.

.In this position of .thestructura the pump 54 drives the oil .Ilowing into .its inlets 56 and 51 from the lower end of .the jack cylinder 6. A port 13 in such cylinder is connected by a conduit 14 to an opening 16 .in the casing 5I of the main valve and inthe position of the valve, shown in Figure 1low occurs through such valve into an outletopening 11 joined'by a loop pipe 18to the twoinlets 56 and51. The pressure imposed upon .the chamber 19 ,of the main valve is carried by a duct 8l .through a hand valve 82 provided with a manual control 83 to a pipe 84 connected to a chamber 86. Therein it is effective upon a.piston,81.xed-on.one end of the poppet .valve 12 and .normally urges such valve open. Adrain Vlinef 4extends vfrom the chamber 86 and a drain .line ..89 extends from the valve 82.to thetankl. Thus in the position of the parts shown in Figure 1, thepiston 1 descends because Vthe .motor -or engine driven pump 5 4 withdraws oilfrom beneath thepiston and transfers it into the tank .42. Y et, as vpreviously-described, whenthe vpiston travels over the operative.one of ,the valves i8, I9 Yor 20, the cycle is interrupted .by .theshifting of the auxiliary or pilot valve and the main valvecorrespondingly is shifted to -reverse the now -andsend it in the opposite direction as willappear from the description of Figure 2.

Thereversal of the main .valve under the control of the pilot valve is eifectuated bya novel mechanism not immediately or-directly dependentiipon the hydraulicsystem which interconnects the4 pump 54,:thejackfcylinder-6 andthe storage or balancing .tank 42. In -accordance with this'inventiomthe hydraulic uid IUI within the auxiliary tank or drainage or scavenge tank I6 is utilized for this purpose. To this-end, I provide anfauxiliary oil-pump |02, located near -the tank I 6 and connected -to it 'through a conduit- |03 in which a hand valve |04 is disposed. The pump I 02 is a pump of the positive displacement type. It is not a centrifugal pump or a pump which has a variable or undetermined amount of slip. Rather it is a pump which is of the metering or predetermined dis-placement type so that the amount of oil flowing through i't in a given time at a known speed is known or established.

There rare various ways of regulating the output or effective output of the auxiliary pump |02. The pump |02 can be driven by the motor 55 or it can be run by a separate source of power |05, itself readily controllable. In either case the auxiliary pump |02 discharges a measured or lpredetermined amount of liquid under all usual operating conditions. The pump- |02 is usually operated upon the same liquid utilized elsewhere in the hydraulic system. When a change in temperature and a corresponding change of viscosity occurs in the main body of oil 43 used directly to actuate the pumping jack, there may be a similar and quite comparable change in viscosity of the oil passing through the pump |02. All structures depending for their timing upon the rate of oil 110W through pipes or orices likewise vary and may vary differently so that their relative timing is changed, and the jack reversal points change erratically.- But all mechanisms responsive to the quantity of oil displaced by the auxiliary pump |02 operate at the same relative point as before despite the viscosity change. If, for example, the oil viscosity decreases due to a general rise in temperature, the pump 54, largely because of orice effects, is effective to discharge at a faster rate. When the pump |02 is driven in synchronism with the pump 54, it also, due largely to orice effects also discharges at a faster rate, but the relationship of the timing is retained so that the reversal points remain the same, and the jack piston maintains its stroke length in the cylinder.

Oil discharged from the pump |02 passes into a line I 06. A relief valve I'I is disposed between the line |06 and the tank` IB by ducts |08 and |99, respectively, and is preferably provided with a pressure spring III so that the pressure within the line |06 can be set at a maximum value and excessive pressure will be bled off to the auxiliary tank I6. Oil flowing through the pipe |06 continues at not to exceed a maximum pressure to a port |I2 in the housing of the auxiliary valve. In the position of the valve shown in Figure 1, this oil travels from the port II2 between lands I I3 and ||4 to an outlet port I I6 from whence it flows through a conduit II'I into a chamber IIB at one end of the main valve 5 I. Pressure within the -chamber |I8 is effective upon a plunger ||9 at one end of the bobbin 53 and is therefore eiective to maintain or translate the bobbin into its left hand position as shown in Figure 1, providing the pressure at the other end of the bobbin is suitable.

When the bobbin is disposed as shown in Figure 1, the plunger |2| at its opposite end within the chamber |22 is in communication by means of a pipe |23 with a port |24 in the auxiliary valve casing. This is disposed between the lands 36 and I I3 in the right hand position of the auxiliary valve. Flow from the port |24 is through the auxiliary valve between the lands 36 and ||3 out through a port |25 into a line I 21 leading back to the auxiliary tank I5. Since the tank I is normally maintained under atmospheric pres-y sure, the chamber |22 is likewise subject to atmospheric pressure. The superior pressure within the chamber I I8 is effective to situate 'the main valve as shown in Figure l.

The only other possible means for variation of the pressure within the chambers I I8 and |22, arises out of certain :connecting lines. Extending into the chamber IIS is a sleeve I3I communicating through a vlin-e f|32 with a pipe |33. Similarly a sleeve |34 extends into the compartment |22 and is connected by a line I 36 to the pipe |33. A manual valve |31 governs iiow into a valve casing |38, within which a poppet valve |39 is disposed. The lower end or the poppet valve is connected by a stem |4| to a float I 42 operating in the body of oil |0I within the tank IG. When the float |42 is high because the oil level in the tank f8 is high, the poppet |39 is closed and the only possibility of iiow from either of the chambers IIS or |22 is into the tank 42. When, however, the oil level |0I is low, the iloat |42 drops, the poppet I 39 opens and if the hand valve |37 is open, as it normally is, oil can flow from either of the chambers IIS or |22 into the tank I5 as makeup. The actual iiow of oil from the valve housing |33 is through a pipe |43 and thenc through a filter |44 and a nal pipe |46 into the tank. If the lter is clogged and its resistance is great, iiow is alternatively through a line I 41 and a relief valve |40 and a connecting line |40.

In this way a level of liquid is maintained in the auxiliary tank I5 so that there is always adequate oil for the pump |62 to actuate the pilot valve and produce a constant eiect upon the main valve. That is, when the pilot valve shifts to an extreme position, for example as shown in Figure l, and the auxiliary pump |02 supplies oil through the pilot valve to the chamber IIB in order to shift the main valve, the rate at which the main valve shifts depends entirely upon the output of the auxiliary pump |02 which in turn is related to the rate at which the main body of oil iiows from the cylinder 6 through the main pump 54- and into the tank 42. The motion of the main valve is independent of the temperature or viscosity or other variable characteristics of the oil flowing through the main valve. Rather, it is responsive only to the operation of the auxiliary pump. Since this is a metering or positive displacement pump, the motion of the main valve is precisely regulated despite iiuctuations in operating conditions.

After the piston 'I has uncovered one of the ports 2| and has caused a shift in the position of the auxiliary valve, the Valve occupies the location shown in Figure 2. Then iiow from the auxiliary pump |02 is directed through the port |I2, not into the port I I0 any longer, but rather into the port |24 and into the line |23 so that a pressure is exerted through it upon the chamber |22. This pressure likewise is communicated through the duct I 36, to provide makeup oil if required, although if it is excessive in amount, it opens a relief valve |5I so returning excess to the main tank 42 in the event a manual valve |52 is open as it normally is. The pressure exerted in the chamber |22 is effective to overcome the pressure within the chamber I I3. The same shift of the auxiliary valve which permits the pressure to be exerted upon the chamber I 22, likewise connects the port I|| with a port |53 in the auxiliary valve housing joined by a pipe 554 with the duct |21, the drain line returning to the atmospheric pressure tank I5. Extra or dis charge :duid from the chamber ||81returnsto the tank I6 and the Vmain valve readily makes Y its shift into the opposite extreme position. In this opposite extreme position, the .two lands 6| and 62 span the ports 59 and 16, so that theflow is then from the outlet ofthe pump 54 under pressure through the line 14.and the port 13 into the bottom of the cylinder 16 beneath the piston 1. Since this is high pressure, it lifts-the piston 1 and the sucker or polish rod 8.

fDuring the time Ythat the piston 1 is rising, the main pump 5,4 isfdriven to withdraw oil fromfthe tank 42 through the open poppet valve 12 and the duct 1| and then upwardly (in Figure 2) through the line 69 to the port 63. The ow then is through themain valvebody between the plunger |2| and-the land 6| and out through a port |55 into the line 18 communicating with bothof the pumpinlets 56 and 51. The ow is then outwardly from the pump through the line 58 into the port 59 and to the jack cylinder 6.

If during the pump operation the-pressure differential between the pump inlets and 'the outlet 54,should be excessive, itis relieved. The outlet pressure is exerted through a line |51 upon a poppet relief valve |58 to displace the valve t0- ward the right in Figure 2, thus uncovering an opening into a chamber |59, affording a short circuit through a conduit |6| to the pipe `'18, and allowing the excess oil to ilow back to the pump inlet 56. In this way differential pressure is prevented from exceeding a set value. Theamount of pressure difference is established by a coil spring |82 provided with a regulator |63 so that the spring is effective upon the plunger |58.

Leakage and drainage from the casing |64 enclosing the relief valve ows to the auxiliary oil tank |6 through a line |66, and means are provided for actuating the poppet valve r| 58 other than by excessive pressure within the pump outlet 54. A pressure line |61 is connected to the line 4| in communication with the body of oil 43 within the tank 42. lNormally this pressure is kept vfrom the pressure relief valve by a hand valve |68, but when the hand valve is opened to a vposition opposite that shown in Figure l, pressure fluid flows through a line |69 into a chamber |1v| in the relief lvalve and it then displaces an enlarged piston |12 to the right (as seen in Figure 2) against the urgency of the spring |62.

When the valve |58 is to be restored Vto its former position, the valve |68 is shut. This action then affords communication between the line |69 and a drain line |13 joined to the line |66 and leading back tothe auxiliary-tank |6. When the valve |68 is shut, the pressure uid inthe chamber |1| discharges to atmospheric pressure and the poppet valve 4|58 shuts under the superior urgency of the spring |62. The manual control of the relief valve is provided for starting and emergency purposes and normally the spring-pressed valve |58 .automatically controlls excessive pressure. Thus the piston 1 is driven upwardly by the operation of the main pump 54 at a controlled rate since the pressure of the oil cannot be excessive.

As the piston 1 ascends in the upper portion of its stroke, it passes over a series of control apertures |16, |11, |18, |19 vand |80 inclusive. Each of these apertures is appropriately connected by a suitable duct |82, |83, `|84, |85 and 'f duct I4 and the Icheck valve |1 to the auxiliary tank I6. This is an emergencyovertravel safety device and normally does-not come into loperation.

Normally the upper/strokelimt control valve |88 is arranged so that a rotatable plug l|88 therein is disposed yin anyone of ve selected positions. Each of these positions is 4in alignment `with any selected one of the ducts |82, |83, |84, |85 and |86 and establishes communication with such duct and a commoncommunication conduit |9|. Joined to the casing of the Valve |89 is a-pipe |92 leading through a check valve I|93 -to the Vpipe 20. In any one of -the selected positions of the selector valve |89, the piston 1 uncovers the vappropriate one of the apertures |16, |11, |18, |19 or |80 and permits pressure fluid then to flow through the selector valve and through the collector conduit |9| into the pipe |92. 'Ihat pressure opens the check valve |93 and imposes pressure through the line 28 and the valve casing 29 upon the spool 38 of the pilot valve. The pressure so exerted within the compartment '33 translates the auxiliary valvefrom its position shown in Figure-2 toward the right into its position shown in Figure l. During this time the chamber in which `the plunger 31 is disposed is-connected through'one line 3,9 4to the balancing tank 42.

During the upstroke of the piston -1, the pump 54 maintains a pressure within the cylinder .-6 in excess of the pressure -within the balancing tank 42. The area of the-spool 36 being several times the area of the vplunger 31, a prompt translation of the auxiliary valveoccursas soon as the piston 1 rises above whichever .of the cylinder apertures is in communication through the selector valve |88 with the auxiliary valve housing.

`When theauxiliary valve is so translated, the auxiliary pump |02 `isithen effective to discharge liquid at a predetermined or set rate through the inlet port H2. Instead of continuing through the outlet port |24 to the left hand end of the main valve, it immediately is shifted to ow between the lands ||3 and ||4 into the outlet port ||6 and so to the right hand end of the main valve. This translates the main valve from its right hand position (shown in Figure 2) back into its left hand position as shown in Figure 1. The speed of the translation or return of the main valve back to its original position is, however, entirely dependent upon the speed of operation of the auxiliary pump |02,'so that the reversal of vmotion of the main piston .1, in changing from its up-stroke back to its down-stroke is at a corresponding rate. This is substantially independent of oil viscosity and of temperature conditions and hence imposes no more than the designed or predetermined stress upon the pump or sucker rod 8.

When the motion has been reversed at the upper end of the stroke, the parts are restored to their initial positions as the piston 1 descends. This is because fluid is again transferred by the main pump 54 from the cylinder 6 back into the balancing tank42. The motion reversalrepeats as the piston 1 moves nearer the lower end of the cylinder and in turn uncovers the effective one of the ducts 2|. The complete cycle is inclusive of two reversals, one at the top and one at the bottom of the stroke. Both of the reversals are governed as to speed or rate of accomplishment by the speed or rate of displacement of the auxiliary pumpand are suitably controlled by an independent means,

that is, the pump |62, whether it is driven by the motor 55 or a separator motor |05, and are independent of random variations which otherwise produce erratic and undesired operation of the pumping jack.

I claim:

1. A hydraulic pumping jack control comprising a jack cylinder, a first oil pump, means for connecting said pump to pump oil alternatively into or out of said cylinder, a hydraulic displacement device having an unobstructed inlet and an unobstructed outlet and actuated by hydraulic fluid for operating said connecting means, and a positive displacement second oil pump for supplying hydraulic fluid to said hydraulic displacement device at a predetermined rate.

2. A hydraulic pumping jack control comprising a jack cylinder, a irst oil pump having an inlet and an outlet, a valve casing, means connecting said casing with said inlet and said outlet, a conduit connecting said casing with said cylinder, a valve in said casing for connecting said conduits to said inlet connecting means or said outlet connecting means, a hydraulic displacement device having an unobstructed inlet and an unobstructed outlet for operating said valve, and a positive displacement second oil pump for operating said hydraulic displacement device at a predetermined rate.

3. A hydraulic pumping jack control comprising a jack cylinder, a first oil pump having an inlet and an outlet, means for interconnecting said rst pump and said cylinder, said means including a valve in a first position connecting said cylinder and said inlet and in a second position connecting said cylinder and said outlet, a hydraulically expansible device having an unobstructed inlet and an unobstructed outlet for moving said valve between said positions, a positive displacement hydraulic second pump, means for driving said second pump at a predetermined rate, and means for hydraulically connecting the outlet of said second pump to said hydraulically expansible device.

4. A hydraulic pumping jack control comprising a jack cylinder, a first oil pump having an inlet and an outlet, means for interconnecting said rst pump and sai-d cylinder, said means including a valve in a rst position connecting said cylinder and said inlet and in a second position connecting said cylinder and said outlet, a hydraulically expansible device having an unobstructed inlet and an unobstructed outlet for moving said valve between said positions, a I

positive displacement hydraulic second pump, means for driving said second pump at a predetermined rate, means including a pilot valve for hydraulically connecting the outlet of said second pump to said hydraulically expansible device, and means responsive to pressure in said cylinder ior operating said pilot valve.

5. A hydraulic pumping jack control comprising a jack cylinder, a piston in said cylinder, aA

first oil pump having an inlet and an outlet, means for interconnecting said iirst pump and said cylinder beneath said piston, said means including a valve in a iirst position connecting said cylinder and said inlet and in a second position connecting said cylinder and said outlet, a hydraulically expansible device having an unobstructed inlet and an unobstructed outlet for moving said valve between said positions, a positive displacement hydraulic second pump, means for driving said second pump at a predetermined rate, means including a pilot valve for hydraulically connecting the outlet of said second pump to said hydraulically expansible device, and means responsive to the position of said piston in said cylinder for operating said pilot valve.

6. A hydraulic pumping jack control comprising a jack cylinder, a rst hydraulic pump having an inlet and an outlet, means for driving said iirst pump, means for interconnecting said first pump and said cylinder, said means including a valve in a rst position connecting said cylinder and said inlet and in a second position connecting said cylinder and said outlet, a hydraulically expansible device having an unobstructed inlet and an unobstructed outlet for moving said valve between said positions, a positive displacement second hydraulic pump driven at a predetermined rate, and means for hydraulically connecting the outlet of said second pump to said device.

7. A hydraulic pumping jack control comprising a jack cylinder, a balancing tank, a pump effective to transfer oil between said cylinder and said tank, a valve for controlling the direction of said transfer, a hydraulic actuator for said valve, said actuator operating by hydraulic displacement and having an unobstructed inlet and an unobstructed outlet, and means for pumping hydraulic fluid through said inlet and said outlet at a constant rate to displace said actuator at a constant rate.

IRA MORGAN WHITE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,906,965 Hobson May 2, 1933 1,910,766 Hobson May 23, 1933 1,943,061 Douglas Jan. 9, 1934 2,069,122 Weaver Jan. 26, 1937 2,167,623 Britter Aug. 1, 1939 2,185,448 Suter Jan. 2, 1940 2,276,358 Vickers Mar. 17, 1942 2,325,138 Kyle et al July 27, 1943 2,331,337 Meyer Oct. 12, 1943 2,355,669 Moser Aug. 15, 1944 2,367,248 Vickers et al Jan. 16, 1945 

